Tunable light sources are useful for many applications. Among them are Swept-Source Optical Coherence Tomography (SS-OCT) where the wavelength is swept back and forth fast between an upper and a lower wavelength. Other applications require DC tuning (i.e. setting the wavelength to a desired value and maintaining it for a certain time for a measurement) or sweeping at various frequencies and/or with different sweep characteristics etc.
Various methods have been employed to achieve swept light sources (in this text, generally the term ‘light’ relates to electromagnetic radiation not only in the visible range, but also in the near- and mid-infrared and in the near-UV, in particular to electromagnetic radiation in the range between 300 nm and 2000 nm). Among these are light sources in which a Micro-Electrical-Mechanical System (MEMS) is used for wavelength tuning. As, for example, disclosed in WO 2010/111795 A1, a grating can be used in a Littrow configuration—the incident beam and the diffracted beam are collinear (or coaxial)—but the wavelength sweep is not caused by a movement of the grating but by moving the beam incident on the grating.